R wave undersensing caused by an algorithm intended to enhance sensing specificity in an implantable cardioverter defibrillator

This article reports on a case of ventricular undersensing despite normal R wave amplitudes during sinus rhythm in an ICD patient. Undersensing of ventricular signals was noted without any evidence of lead dislocation or variation in signal amplitude. Undersensing was due to an exceptionally small R wave signal width and a feature of the Biotronik sensing algorithm designed to avoid oversensing. This algorithm, intended to enhance the sensing specificity of the device, requires registration of two consecutive points above the maximum programmed sensitivity for a ventricular sense event. After modifying the algorithm to a single point registration undersensing disappeared.     

Potential Hazards of Fixed Gain Sensing and Arrhythmia Reconfirmation for Implantable Cardioverter Defibrillators

Appropriate sensing of ventricular tachycardia (VT) and ventricular fibrillation (VF)is of paramount importance for safety of patients with implanted cardioverter defibrillators (ICDs). Recently, the Guardian^R ATP 4210, a new third generation ICD that uses programmable but fixed sensing during sinus rhythm and doubles its sensitivity settings when VF is detected, to a maximum programmable sensitivity of 1 mV, has been tested in phase I and II clinical trials. A reconfirmation algorithm of this ICD confirms the presence of VT or VF prior to therapy. This case report describes undersensing of VF in a patient with the Guardian^R ATP 4210 at the maximum programmed sensitivity of 1 mV. Inappropriate episodes of asystole and prolonged bradycardias were also observed in this patient due to shortcomings in the reconfirmation algorithm design. Reoperation was required, with positioning of a new endocardial sensing lead to correct the undersensing of VF. This, however, did not correct asystolic pauses following antitachycardia pacing or spontaneous tachycardio termination prior to therapy. This case report highlights the hazards of fixed gain sensing for implantable ICDs and a potential limitation of a specific tachyarrhythmia reconfirmation algorithm used in this device.     

Improved Sensing Signals After Endocardial Defibrillation with a Redesigned Integrated Sense Pace Defibrillation Lead

Adequate sensing is a basic requirement for appropriate therapy with ICDs. Integrated sense pace defibrillation leads, which facilitate ICD implantation, show a close proximity of sensing and defibrillation electrodes that might affect the sensing signal amplitude by the high currents of internal defibrillation. In 99 patients, we retrospectively examined two integrated sense pace defibrillation leads, eitherboth with a distance of 6 mm between the tip of the lead (sensing cathode) and the right ventricular defibrillation electrode (sensing anode) or one with a distance of 12 mm. Three seconds after a shock of 20 J, mean sensing signal amplitude during sinus rhythm (SR) decreased from 10.5 ± 4.3 mVto 5.1 ± 3.7 mV (P < 0.001) for the 6-mm lead, but showed no significant decrease for the 12-mm lead. The degree of signal reduction was inversely related to the time passed since defibrillation. Significant differences in reduction of sensing signal amplitude concerning monophasic and biphasic shocks could not be observed. Mean sensing signal amplitude of VF after shocks that failed to terminate it decreased in the same order as during SR (from 8.3 ± 4.1 mV to 4.1 ± 3.2 mV), but resulted in no failure of redetection during ongoing VF. DFTs did not differ for the 6-mm and the 12-mm lead. In conclusion, close proximity of the right ventricular defibrillation coil to the sensing tip of an integrated sense pace defibrillation lead causes energy and time related reductions in sensing signal amplitude after defibrillation, and might cause undersensing in the postshock period. A new lead design with a more proximal position of the right ventricular defibrillation coil avoids these problems without impairing DFTs.     

Implant and Long-Term Evaluation of Atrial Signal Amplification in a Single-Lead ICD

Background: In patients without clinical indications for pacing the use of a single-lead implantable cardioverter defibrillator (ICD) implementing atrial sensing capability with proper signal amplification management may represent a useful therapeutic option, combining the positive features of both single and dual-chamber devices. The aim of the study was to evaluate the atrial signal amplification and its long-term stability in a single-lead ICD system adding atrial sensing to a standard single-chamber ICD. Methods: P-wave amplitudes were collected and compared at implant both with a conventional external device ("unfiltered" P wave) and telemetrically with the implanted ICD ("filtered" P wave). Filtered/unfiltered P-wave ratio (amplification factor, AmF) was evaluated at implant and during follow-up. Results: In 43 enrolled patients (38 men, age 64 ± 16 years), the mean filtered P wave at implant was significantly higher than the unfiltered P wave (3.85 ± 0.81 mV vs 2.0 ± 1.49 mV; P < 10(-11) ), with a mean AmF value of 2.77 ± 1.62. In seven patients with atrial fibrillation at implant, the AmF was higher (4.62 ± 1.94) than in patients in sinus rhythm (2.41 ± 1.30; P < 0.001). A significant linear correlation was found between the inverse of P wave and the AmF (R = 0.82, P < 0.00001). In 25 patients followed for 384 ± 244 days, atrial undersensing was never documented and AmF did not change from implant (3.19 ± 1.82; P = 0.24), also in different body position and breathing conditions. Conclusions: The single-lead ICD system evaluated reliably amplified P-wave amplitudes by a factor of about three, maintaining this performance during the observed follow-up. (PACE 2012; 35:1119-1125).     

Failure of a Second and Third Generation Implantable Cardioverter Defibrillator to Sense Ventricular Tachycardia: Implications for Fixed-Gain Sensing Devices

Failure to sense ventricular tachycardia and/or ventricular fibrillation by implantable cardioverter defibrillators (ICDs) is rare. We report a case in which persistent undersensing of monomorphic and polymorphic ventricular tachycardia occurred with a second and third generation ICD using fixed-gain sensing. This occurred despite adequate R wave sensing during sinus rhythm. The use of an endocardial sensing lead did not correct the problem. Failure to sense ventricular tachycardia in the third generation device with fixed-gain sensing occurred late after implantation and was discovered only at follow-up electrophysiology testing of the ICD. This problem could not be corrected by reprogramming of the device, and was not related to lead dislodgement. Placement of a new device with an automatic-gain sensing algorithm and use of previously implanted epicardial leads with better sensing characteristics provided appropriate sensing of ventricular tachyarrhythmias. The case illustrates the importance of testing the sensing of all ventricular arrhythmias in patients with fixed-gain ICD's. Follow-up electrophysiology testing and evaluation of epicardial and endocardial leads may be necessary in certain cases to ensure adequate sensing of ventricular tachyarrhythmias late after implantation.     

Transcutaneous T Wave Shock: A Universal Method for Ventricular Fibrillation Induction

Our objective was to develop a universal noninvasive method for VF induction. ICD implantation requires VF induction. Conventional rapid ventricular stimulation may fail to induce VF. Some ICDs can deliver low energy shocks on the T wave to induce VF. We hypothesized that an external dual chamber pacemaker and an external defibrillator could be configured to allow reliable VF induction with any ICD system. A surface ECC signal was delivered to the atrial channel of an external dual chamber DDD pacemaker. The 'AV' delay was adjusted so that the ventricular output of the pacemaker was delivered to an external defibrillator synchronized to deliver 5–50 J. Twenty-six patients at ICD implant or follow-up had VF induced in native rhythm (sinus rhythm or atrial fibrillation), or during a ventricular pacing train (3–8 beats at cycle length 500–880 ms). VF was successfully induced in 14 of 25 (56%) patients in native rhythm; and in 16 of 17 (94%) patients during pacing (P = 0.013). VF induction success rate was 36% in native rhythm (31/86 attempts) and 88% during pacing (69/78 attempts) (P < 0.001). The 'R' to shock interval was 269 ± 31 ms in native rhythm and 257 ± 48 ms during pacing. Energy delivered from the external defibrillator was 19 ± 3 J in native rhythm and 21 ± 6 J during pacing. We concluded that VF induction by synchronizing a small external shock to the T wave is a fast, effective way to reliably ensure arrhythmia induction with any ICD at implant or follow-up. This method is more successful during pacing than in sinus rhythm.     

Chronic experiences with a single lead dual chamber implantable cardioverter defibrillator system

Monitoring of atrial rhythm in patients implanted with ICDs may improve accuracy in identifying supraventricular arrhythmias and, therefore, prevent inappropriate therapies. Since difficulties were found in dual chamber ICDs with separate leads, a new designed single lead dual chamber ICD system was tested. Twenty-five patients implanted with a Deikos A+ (single coil defibrillation lead with two atrial sensing rings combined with a dual chamber ICD with a high amplifying atrial channel) were tested. Atrial and ventricular signals were analyzed during sinus rhythm (SR) and sinus tachycardias (STs), atrial flutter and AF, and VT or VF. Follow-ups were performed after 1, 3, 6, 9, and 12 months after implantation. Analysis of EGM amplitudes of stored episodes revealed that atrial signals during atrial flutter (2.1 +/- 0.51 mV) were comparable to those of ST (2.2 +/- 0.5 mV). Atrial amplitudes during AF were significantly lower (0.81 +/- 0.5 mV, P<0.01). During VF atrial "sinus" signals (2 +/- 0.8 mV) were stable. Ventricular parameters did not differ from a standard ICD lead; defibrillation threshold was 11.4 +/- 4.5 J (16 patients). During intraoperative and prehospital discharge measurements, 97.1% of SR-P waves and 99.2% of atrial flutter waves were detected correctly. In AF 91.11% of atrial signals were detected. Analysis of 505 stored episodes showed that 96.8% of ST and 100% of atrial flutter and 100% of AF episodes have been classified correctly and no underdetection of VT/VF was found. The first experiences with the new VDD-ICD system show an increase of the specificity to detect ventricular tachycardias to a level comparable to dual chamber ICDs with two leads. The reliability of this system has to be proven in a prospective randomized study.     

Variability of atrial sensing during exercise in a patient with a dual chamber ICD caused inappropriate ICD discharges

We present the case of a patient with a dual chamber implantable cardioverter defibrillator (ICD) who experienced inappropriate ICD discharges during exercise. Interrogation of the ICD revealed intermittent atrial undersensing during exercise that was responsible for the erroneous classification by the ICD of sinus tachycardia as ventricular tachycardia. Monitoring of the intracardiac electrograms and Marker Channels during an exercise test confirmed a marked decrease in P wave amplitude during exercise. By increasing the atrial sensitivity setting the problem was resolved.     

Implantation strategy of the atrial dipole impacts atrial sensing performance of single lead VDD pacemakers

Intermittent atrial undersensing is observed in a considerable percentage of patients with single lead VDD pacemakers. Analyzing the 2-year data of the Saphir Multicenter Follow-Up Study, the authors investigated predictors for the occurrence of undersensing. The study included 194 patients with high degree AV block who received a VDD pacemaker system with an identical sensing amplifier. Placement strategy of the atrial dipole was left to the discretion of the implanting physician. At the final position, atrial potential amplitudes were measured during deep and shallow respiration. Atrial dipole position was determined by intraoperativefluoroscopy subdividing the right atrium in a high, mid, and low portion. Undersensing was defined by evidence of at least one not sensed P wave during Holter monitoring or exercise testing and by the presence of 0.1-0.2 mV amplitudes in the P wave amplitude histogram of the pacemaker. Incidence of undersensing was 25.8%; 9.3% of patients showed frequent (> 5%) or symptomatic undersensing. Patients with undersensing were older (76.6 +/- 10.6 vs 64.2 +/- 14.8 years), showed a lower minimum of intraoperative atrial potential amplitude (P(min) 0.86 +/- 0.64 vs 1.43 +/- 0.77 mV), a wider range of potential amplitude (deltaP 1.71 +/- 1.44 vs 0.94 +/- 0.84 mV), and a higher incidence of dipole placement in the low right atrium (50.0% vs 11.1 %, P < 0.001 for all comparisons). In a multivariate regression analysis, patient age > 66 years, Pmin < 0.6 mV, > 1.3 mV and atrial dipol placement in the lowright atrium were independently predictive for undersensing. Minimal atrialpotential amplitude, range of potential amplitude, and atrial dipole position influence atrial sensing performance in single lead VDD pacing. Thus, implantation guidelines should reflect these rules to improve the outcome of VDD pacemaker recipients.     

Acute Atrial Endocardial P Wave Amplitude and Chronic Pacemaker Sensitivity Requirements: Relation to Patient Age and Presence of Sinus Node Disease

Data are reviewed from 88 patients who received double, passive-fixation unipolar endocardial leads for DDD pacemaker treatment. Identical electrodes were used in the right atrium and the right ventricle. Intra-atrial P wave amplitudes, intraventricular QRS complex amplitudes, and atrial and ventricular pacing thresholds were determined at implantation. The intra-atrial P wave amplitudes were not significantly correlated to the intraventricular QRS complex amplitudes. No significant correlation was found between the atrial stimulation thresholds and the ventricular pacing thresholds. The intra-atrial P wave amplitude showed a significant inverse and logarithmic correlation with patient age (P = 0.007). Furthermore, patients with sinus node disease had significantly lower intra-atrial P wave amplitudes (P = 0.04) than patients without this abnormality. The acute atrial and ventricular pacing thresholds and the intraventricular QRS complex amplitude were not correlated to patient age or presence of sinus node disease. Patients requiring higher atrial amplifier sensitivity settings during follow-up were significantly older (P less than 0.05) than those in whom lower atrial sensitivities were sufficient. A postoperative attenuation of the atrial electrogram was detectable by sensitivity programming procedures in 29 of the patients (35%). This phenomenon did not significantly relate to patient age or presence of sinus node disease. No case of permanent atrial undersensing occurred. It is suggested that the lower intra-atrial P wave amplitudes in older patients and patients with sinus node disease reflect degenerative changes in the atrial myocardium. The statistical relations found appear to motivate special attention to atrial sensing in these patient groups.     

Comparison of Bipolar Atrial Electrogram Amplitude in Sinus Rhythm, Atrial Fibrillation, and Atrial Flutter

Automatic mode switching pacemakers revert to non-atrial tracking modes in response to sensed atrial tachyarrhythmias. It is unclear how atrial electrogram amplitudes in sinus rhythm compare to those during atrial tachyarrhythmias. In this study, peak-to-peak bipolar atrial electrogram amplitudes were measured during sinus rhythm and either atrial fibrillation or atrial flutter in 69 patients. The mean atrial electrogram amplitudes were 1,59 ± 1.36 m V during sinus rhythm and 0.77 ± 0,58 mV during atrial fibrillation (P < 0.0001) for 25 patients with atrial fibrillation and 1.81 ± 2.07 mV during sinus and 1.5 ± 1.81 mV(P < 0.0001) for 44 patients with atrial flutter. The mean electrogram amplitudes during both atrial fibrillation and flutter correlated significantly with amplitudes during sinus rhythm (R = 0.79, R = 0.94. respectively, both P < 0,0001). The coefficient of variance of individual electrogram amplitudes was greater in atrial fibrillation than sinus (P < 0.0001). By comparing 20th percentile electrogram amplitudes in atrial fibrillation and flutter to mean sinus amplitudes, intermittent very low electrogram amplitudes (< 0.3 mV) were more likely during atrial fibrillation and flutter if the mean sinus electrogram amplitudes were < 1.5 mV and < 0.5 mV, respectively (P < 0.01). Eightieth percentile electrogram amplitude values in atrial fibrillation and flutter were equally likely to exceed mean sinus amplitude values in respective patients, in conclusion, mean atrial electrogram amplitudes during atrial fibrillation and flutter are less than but correlated to sinus rhythm electrogram amplitudes. Very low amplitude individual electrograms during these atrial arrhythmias are associated with low mean sinus rhythm electrogram amplitudes. These findings may have implications for the programming of permanent dual chamber pacemakers in patients with paroxysmal atrial fibrillation and flutter.     

True bipolar and integrated bipolar sensing and detection by implantable defibrillators

Introduction: Sensing and detection can be performed in true bipolar or integrated bipolar configuration by implantable defibrillators. New Medtronic generators (Medtronic Inc., Minneapolis, MN, USA) can be configured so that the sensing function of the device can be either true bipolar or integrated bipolar. We compared the sinus rhythm R‐wave amplitude and detection time of induced ventricular fibrillation (VF) at implant (acute phase), and sinus rhythm R‐wave amplitude 3 months or more after the implant (chronic phase) in these two configurations. Methods: Twenty‐eight patients were studied in the acute phase, and a subgroup of 15 patients was tested in the chronic phase. The generators were Medtronic model numbers D224VRC, D224TRK, D224DRG, D284VRC, D284TRK, and D284DRG. The leads were Medtronic 6947 or 6935. Sensing was evaluated by recording the electrogram and measuring the R‐wave peak‐to‐peak amplitude in the two configurations. Detection was evaluated by measuring the detection time in the two configurations in two consecutive inductions. The detection time was measured on programmer paper from the marker of the T shock to the marker of VF. Results: The acute‐phase values were: R wave in true bipolar configuration 13.9 ± 7.1 mV, R wave in integrated bipolar configuration 13.6 ± 6.9 mV (p = 0.38),VF detection time in true bipolar configuration 3.12 ± 0.39 seconds, and VF detection time in integrated bipolar configuration 3.17 ± 0.39 seconds (p = 0.52). Conclusions: Sensing and detection at implant were not significantly different between the true bipolar and the integrated bipolar configurations for the tested leads and generators. (PACE 2011; 34:1561–1568)     

Multicenter Experiences with a Single Lead Electrode for Dual Chamber ICD Systems

Monitoring of atrial signals improves the accuracy in identifying supraventricular tachyarrhythmias to prevent inappropriate therapies in patients with implantable ICDs. Since difficulties due to the additional atrial lead were found in dual chamber ICD systems with two leads, the authors designed a single pass VDD lead for use with dual chamber ICDs. After a successful animal study, the prototype VDD lead (single coil defibrillation lead with two additional fractally coated rings for bipolar sensing in the atrium) was temporarily used in 30 patients during a German multicenter study. Atrial and ventricular signals were recorded during sinus rhythm (SR), atrial flutter, AF, and VT or VF. The implantation of the lead was successful in 27 of 30 patients. Mean atrial pacing threshold was 2.5 +/- 0.9 V/0.5 ms, mean atrial impedance was 213 +/- 31 ohms. Atrial amplitudes were greater during SR (2.7 +/- 1.6 mV) than during atrial flutter (1.46 +/- 0.3 mV, P < 0.05) or AF (0.93 +/- 0.37 mV, P < 0.01). During VF atrial "sinus" signals had significantly (P < 0.01) lower amplitudes (1.4 +/- 0.52 mV) than during SR. The mean ventricular sensing was 13.3 +/- 7.9 mV and mean ventricular impedance was 577 +/- 64 ohms. Defibrillation was successful with a 20-J shock in all patients. In addition, 99.6% of P waves could be detected in SR and 84.4% of flutter waves during atrial flutter. During AF, 56.6% of atrial signals could be detected without modification of the signal amplifier. In conclusion, a new designed VDD dual chamber lead provides stable detection of atrial and ventricular signals during SR and atrial flutter. Reliable detection of atrial signals is possible without modification of the ICD amplifier.     

Comparative Evaluation of Acute and Long-Term Clinical Performance of Two Single Lead Atrial Synchronous Ventricular (VDD) Pacemakers: Diagonally Arranged Bipolar Versus Closely Spaced Bipolar Ring Electrodes

Floating P wave sensing can be derived from bipolar atrial electrodes with different electrode configurations, although the relative clinical efficacy of these methods of atrial sensing has not been studied. We evaluated 32 sex and age matched patients with advanced AV block who received A V synchronous pacers using either a single lead with diagonally arranged bipole (Unity VDDR, Model 292, Intermedics Inc.) or closely spaced bipolar complete ring electrodes (Them VDD, Model 8948, Medtronic Inc.). The total surface area of the atrial electrodes were 17.2 and 25 mm², and the highest programmable atrial sensitivities were 0.1 and 0.25 mV, respectively. Atrial electrogram amplitude and sensing threshold were evaluated at implant and at each follow-up clinic visit (1, 3, and 6 months), Stability of atrial sensing was assessed during physical maneuvers, treadmill exercise test, and Holier recording. Atrial electrogram amplitude at implantation was higher in the Them VDD (2.08 ± 0.79 vs 1,45 ± 0.59 mV in Unity VDDR; P < 0.05), but the value of atrial sensing threshold was lower during follow-up than Unity VDDR. P wave undersensing was additionally observed with both pacemakers during physical maneuvers and exercise testing (6%-19% of patients). Two and four patients had atrial undersensing on Holter in the Unity VDDR and Them VDD, respectively, and the percentage P wave undersensing were 0.88%± 2.41% versus 3.63%± 8.16%, respectively. Reprogramming of the atrial sensitivity in the Unity VDDR and the use of investigational software allowing 0.18 mV atrial sensitivity to be programmed in the Them VDD substantially reduced the percentage of P wave undersensing on Holter to 0.46%± 1.67% and 0.10%± 0.24%, respectively. Beginning at discharge with a programmed atrial sensitivity level at least twice the sensing margin, the mean atrial sensitivity level was reprogrammed from 0.29 to 0.26 mV for Unity VDDR and 0.33 to 0.24 mV for Them VDD at 6 months. There was no incidence of atrial oversensing. Despite differences in atrial amplitudes at implantation between the diagonally arranged bipole and closely spaced full ring single lead systems, the clinical performances of atrial sensing were similar at an appropriately high atrial sensitivities. The absence of atrial oversensing suggests that single pass VDD pacemakers should probably be programmed at the highest available atrial sensitivity to ensure adequate P wave sensing as guided by physical maneuvers and Holter recording to minimize the need of subsequent reprogramming.     

Serum Creatine Kinase Activity And Sensing Characteristics After Intraoperative Arrhythmia Induction Using Implantable Defibrillator Rate Sensing Leads

In 29 patients (24 men, 5 woman, mean age 57 +/- 14 years) we evaluated the effect of intraoperative arrhythmia induction during implantable defibrillator (ICD) placement using alternating current (AC) applied through the epicardial rate sensing leads on acute and chronic pacing thresholds, electrogram amplitudes, slew rates and serum creatine kinase levels. In 15 patients undergoing new ICD implantation, pacing thresholds, electrogram amplitudes, slew rates, and resistances were measured before and following at least three inductions of ventricular fibrillation (VF) using AC applied through the epicardial rate sensing leads. Fourteen patients who underwent VF induction using AC through the epicardial leads during initial implant (mean time of 31 months previously) underwent ICD pulse generator replacement only with parameters measured as above before and after at least two inductions, and these compared to the values at initial implant. In all 29 patients serum creatine kinase levels were obtained before, immediately following, and at 8, 16, and 24 hours after surgery. No significant change in acute pacing threshold, electrogram amplitude, slew rate or resistance occurred. Chronically there was an expected 154% increase in pacing threshold but no significant change in electrogram amplitude or resistance. Serial serum creatine kinase and MB isoenzyme determinations demonstrated no evidence of myocardial necrosis. We conclude that intraoperative arrhythmia induction during ICD implantation using AC applied through the rate sensing leads is a safe and effective technique.     

Improved Efficacy of Mode Switching During Atrial Fibrillation Using Automatic Atrial Sensitivity Adjustment

Automatic mode switching (AMS) during atrial fibrillation (AF) in a dual chamber pacemaker is dependent on the accurate detection of an atrial electrogram. As atrial amplitude is often reduced during AF compared with sinus rhythm, this may result in failure of the AMS and a rapid ventricular response. In addition, undersensing of AF may result in competitive atrial pacing that sustains AF. We hypothesize that the use of automatic atrial sensitivity adjustment (ASA) may enhance AF sensing in a dual chamber pacemaker. We studied the AMS response with and without ASA of the Marathon DDDR (model 294–09, Intermedics, Inc.) pacemaker in 10 patients with paroxysmal AF. Intracardiac atrial electrograms during sinus rhythm and induced AF were recorded onto an analog tape recorder. They were replayed into the pacemaker to assess the AMS response at various starting atrial sensitivities from 3.5 to 0.8 mV with ASA activated and without. Atrial amplitude was reduced during AF. The higher the initial atrial sensitivity, the better is the AMS response and the lower the incidence of AF undersensing. The percentage of AMS before ASA ranged from 2.1% at an atrial sensitivity 3.5 mV to 95.6% at highest sensitivity of 0.5 mV (P < 0.05). After 10 minutes of ASA, the AMS response was improved from 1.7% to 50.6% and from 9.5% to 50.9% at starting atrial sensitivities of 3.5 mV and 2.5 mV, respectively (P < 0.05 in both instances). Undersensing during AF was also significantly reduced after ASA from 70% to 10% at a sensitivity of 3.5 mV and from 33.8% to 10.8% at 2.5 mV. There was no increase in oversensing. In four patients with paroxysmal AF with an implanted pacemaker, ASA improved AMS response in patients with a low implant atrial amplitude. In conclusion, efficacy of mode switching and AF sensing are dependent on the programmed atrial sensitivity, which can be enhanced with the use of ASA, particularly when P wave sensing during AF is borderline.     

Long-Term Stability of P Wave Sensing in Single Lead VDDR Pacing: Clinical Versus Subclinical Atrial Undersensing

Optimal function of a single lead P wave synchronous rate adaptive ventricular pacing system (VDDR) requires reliable P wave sensing over time and during daily activities. The stability of P wave sensing and the incidence of sensitivity reprogramming in a single pass lead with a diagonally arranged bipole was assessed in 30 patients with complete atrioventricular block over a follow-up period of 12 ± 1 months (range 6 months to 3 years). Atrial sensing was assessed during clinic visits, by physical maneuvers (postural changes, breathing, Valsalva maneuver, walking and isometric exercise), maximum treadmill exercise and Holter recordings. P wave amplitude at implantation was 1.21 ± 0.09 (0.5–3.6) mV, and the atrial sensing threshold remained stable over the entire period of follow-up. Using an atrial sensitivity based on twice the sensing threshold at 1 month, P wave undersensing was found in 2, 4, 3, and 7 patients during clinic visit, physical maneuvers, exercise, and Holter recordings, respectively. Atrial sensitivity reprogramming was performed in three patients based on the correction of undersensing during physical maneuvers. Although eight patients had atrial undersensing on Holter recordings, the number of undersensed P waves was small (total 101 beats or 0.013%± 0.001% of total ventricular beats) and no patient was symptomatic. One patient had intermittent atrial undersensing at the highest sensitivity, but the VDDR mode was still functional most of the time. No patient had myopotential interference at ihe programmed sensitivity. One patient developed chronic atrial fibrillation and was programmed to the VVIR mode. Thus, single lead VDDR pacing is a stable pacing mode in 97% of patients. Because of the large variability of P wave amplitude, the use of a sensitivity margin at least three times the atrial sensitivity threshold will maximize atrial sensing and minimize the need for atrial sensitivity reprogramming (1/30 patients). Physical maneuvers and exercise tests are effective means for rapid assess ment of the adequacy of P wave sensing.     

Oversensing in a Cardioverter Defibrillator System Caused by Interaction Between Two Endocardial Defibrillation Leads in the Right Ventricle

A 53-year-old male patient underwent implantable Cardioverter defibrillator (ICD) implantation with a single lead (Endotak ®) transvenous system due to recurrent episodes of drug refractory ventricular tachycardia. After pulse generator replacement, inappropriate ICD shocks were observed due to muscle potential sensing. Intraoperatively, the old Endotak ® lead could not be extracted; therefore, it was transsected and capped. A new lead was inserted and tested without any problems. At the predischarge test, VF was induced and was followed by ICD shocks during sinus rhythm. In another surgical procedure, the old Endotak ® lead was explanted using a special instrument. The present report demonstrates that two endocardial Endotak ® leads should be avoided, because the leads may disturb each other and be followed by inappropriate ICD discharges.     

Undersensing of Ventricular Fibrillation in a Noncommitted Nonthoracotomy Cardioverter Defibrillator System

Objective: Evaluation of the impact of undersensing on VF detection time and the relationship of undersensing to the programmed shock energy. Background: Failure to reconfirm an ongoing arrhythmia due to undersensing by a noncommitted ICD might prolong the time to therapy. Methods: We measured initial detection times and redetection times at predischarge and at 2 and 6 months in 29 patients (22 men, mean age 60 years) with a noncommitted nonthoracotomy ICD. Telemetry data and output markers were used to analyze each induction. Results: Undersensing hading to failure to reconfirm was present in 44 (11.1%) of 398 episodes of sustained VF and prolonged significantly the median initial detection time from 2.3 seconds (25th and 75th percentiles: 2 and 2.6 s, respectively) to 5.45 seconds (4.3 and 7.35 s. P < 0.0001). One episode required external defibrillation after reconfirmation failure occurred during charging; the total detection time prior to shock was 46 seconds. In a subset of 87 episodes with failed first shocks, the initial detection time was 2.3 seconds (2.1 and 2.8 s) and the redetection time 3 seconds (2.5 and 4.77 s. P < 0.0001). The presence of undersensing prolonged the redetection from 2.6 seconds (2.35 and 3.1 s) to 5.4 seconds (4.53 and 7.35 s, P < 0.0001). Undersensing was more prevalent during the redetection period (P = 0.004) and in episodes of sustained VF in which the first shock energy was higher than 15 f (19.7% vs 5.8%, P < 0.0001). Conclusions: In this automatic defibriliator system, undersensing occurs in 11% of the sustained VF inductions and prolongs detection time significantly. Redetection is longer than initial detection mostly due to the presence of undersensing, the frequency of which is proportional to the programmed energy. The clinical significance of this finding is unknown.     

Determining Optimal Atrial Sensitivity Settings for Single Lead VDD Pacing: The Importance of the P Wave Histogram

In order to provide atrioventricular synchrony, VDD pacing systems require reliable atrial sensing. Variations in atrial signals with exercise and daily activities may lead to undersensing, with loss of physiological pacing. The aim of this study was to determine, for a single lead VDD pacing system, the maximal variation in atrial signals in order to facilitate optimal programming of atrial sensitivity. Fifteen patients underwent implantation of a Vitatron Saphir VDD pacemaker with a Vitatron Brilliant electrode. At a mean (± SD) follow-up of 67.3 ± 38.8 days, resting P wave amplitude was compared with the P wave amplitude histogram obtained from the pacemaker, which recorded atrial signals over the preceding 30 days. Resting P wave amplitude was also compared with P wave amplitudes during variations in posture, respiration, and during exercise. P wave amplitude showed great variation with changes in posture and respiration, but there was no consistent increase or reduction. During exercise, the mean P wave amplitude fell hy 36.6%± 31.3% compared with the resting value (P < 0.05). During daily activities, 22.6% of P wave amplitudes recorded on the P wave histogram were < 0.5 mV. The smallest P wave amplitudes were detected by the P wave histogram in 11 (79%) of 14 patients. These data suggest that atrial sensitivity may need to be programmed higher than that indicated by single readings or exercise. The P wave amplitude histogram is the most reliable indicator of the smallest atrial signal and should be used to opthnize atrial sensitivity settings.